![]() ![]() The phosphate groups, with a pKa near 0, are completely ionized and negatively charged at pH 7. The hydroxyl groups of the sugar residues form hydrogen bonds with water. The backbones of both DNA and RNA are hydrophilic. ![]() Thus, the covalent backbones of nucleic acids consist of alternating phosphate and pentose residues, and the nitrogenous bases may be regarded as side groups joined to the backbone at regular intervals. ![]() ![]() Phosphodiester Linkages in the Covalent Backbone of DNA and RNA The successive nucleotides in DNA and RNA are covalently linked through phosphate-group bridges in which the 5’-phosphate of one nucleotide unit is joined to the 3’-hydroxyl group of the next, creating a phosphodiester linkage (Fig. There is also a wide variety of special-function RNAs, including some called ribozymes that have enzymatic activity. Transfer RNAs (tRNAs) are adaptor molecules that participate in translating the information in mRNA into a specific sequence of amino acids in a polypeptide. Messenger RNA (mRNAs) carry genetic information specifying the sequences of proteins. Ribosomal RNAs (rRNAs) are structural and catalytic components of ribosomes. The storage and transmission of biological information are the only known functions of DNA. Segments of DNA specifying the synthesis of a functional protein or RNA product are called genes. The amino acid sequence of every protein in a cell, and the nucleotide sequence of every RNA, is specified by a nucleotide sequence in genomic DNA. They are also constituents of the nucleic acids, deoxyribonucleic acid (DNA) and ribonucleic acid (RNA). They are the energy currency in metabolic reactions, the essential chemical links in the response of cells to hormones and other stimuli, and the structural components of a variety of enzyme cofactors and metabolic intermediates. to Nucleotides and Nucleic Acids Nucleotides have a variety of roles in cellular metabolism. ![]()
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